Mosaic acral keratosis

"African" acral keratoderma: Further evidence for a single entity. A retrospective study of 42 patients

BACKGROUND

Several phenotypes of non-inflammatory palmar and plantar keratoderma (PPK) have been described in patients of Sub-Saharan African descent. They include keratosis punctata of the palmar creases, marginal keratoderma, also known as acrokeratoelastoidosis or focal acral hyperkeratosis, knuckle pads, other forms of diffuse hyperkeratosis, the very rare "mosaic acral keratosis", and ainhum. A previous survey has shown that these various forms of PPK are particularly frequent in patients of Sub-Saharan African descent and that they commonly occur concurrently, suggesting that they could form part of a single entity called "African" Acral Keratoderma (AAK).

AIM

To assess the validity of the concept of AAK and clarify its main characteristics.

METHODS

A retrospective, descriptive, monocenter study was carried out on patients with AAK seen at our institution between 2009 and 2020.

RESULTS

There were 42 patients (median age 38 years, range: 12-69 years), all of Sub-Saharan African descent. The male-female sex ratio was 0.3. Thirty-three (78%) had diffuse keratoderma, 25 (59%) had marginal keratoderma on their hands and/or feet, 20 (48%) had knuckle pads, 20 (48%) had keratosis punctata of the palmar creases, 3 had ainhum, and 2 had mosaic acral keratoderma. Mixed forms were seen in 76% of the patients (n = 32). Familial histories were reported by 17 patients (40%). Treatment was topical in over 90% of patients and systemic in 9 patients (21%). Ainhum was managed surgically.

CONCLUSION

This retrospective study provides additional evidence for the concept of AAK. A genetic origin is suggested by the familial aggregation of cases.

[Ainhum and "African acral keratoderma": three cases]

BACKGROUND

Ainhum, or spontaneous dactylitis, involves the formation of a gradual constriction in the digital-plantar fold of the fifth toe that leads, after several years, to autoamputation of the digit. This condition is classically distinguished from "true" ainhum, of unknown aetiology and affecting only subjects of African origin, from "pseudo-ainhum", resulting from different causes such as inflammatory constriction or constriction by a foreign body, and finally from ainhumoid palmoplantar keratoderma, which is of genetic origin and occurs for instance in Vohwinkel syndrome. Herein, we report three cases of ainhum in women of sub-Saharan African origin; in addition, all three subjects were also presenting various forms of hyperkeratosis of the hands and feet known to primarily affect subjects of African origin.

PATIENTS AND METHODS

The three patients, aged 30, 48 and 44 years, were respectively from Mali, Guinea and Senegal. They had consulted a dermatologist for violent pain in the fifth toe, which frequently prevented sleep and was inexplicable despite several consultations, and even in one case in spite of surgical investigation. Once the diagnosis had been made, relief was promptly provided for all three patients through Z-plasty to remove the circular constriction around the toe in question. In addition to ainhum, the first patient was also presenting diffuse palmoplantar keratoderma, together with an aspect of acrokeratoelastoidosis on the edges of her hands and feet, and knuckle pads, while the second was presenting diffuse palmoplantar keratoderma and an aspect of marginal acrokeratoelastoidosis, and the third was presenting small knuckle pads.

DISCUSSION

A recent study has confirmed the high incidence of several forms of palmoplantar keratoderma of African origin, as well as frequent association of these different varieties with one another. These consist of diffuse keratoderma having a relatively non-specific aspect, keratoderma punctata of the palmar creases, marginal keratoderma known also as focal acral hyperkeratosis, and acrokeratoelastoidosis, despite the absence of histological evidence, and finally, inverted keratoderma, i.e. affecting the dorsal aspects of the extremities, such as knuckle pads. In the three cases presented here, ainhum was associated with these different forms of acral keratoderma seen chiefly in subjects of African origin.

CONCLUSION

So-called "true" ainhum may be included in a broader group of African acral keratoderma, further reinforcing the unity of this group. Genetic studies are required to enable validation and refinement of these clinical findings.

Acrokeratoelastoidosis

Acrokeratoelastoidosis of Costa is a rare papular palmoplantar keratosis characterized by small round-oval to rhomboid-shaped, yellowish papules most commonly localized to the palmar surface of the hands and sometimes also found on plantar surfaces of the feet. Both autosomal dominant and sporadic forms of the disease have been reported. Histologically acrokeratoelastoidosis is marked by hyperkeratosis and epidermal hypertrophy. Specific stains for elastic tissue reveal characteristic fragmentation and rarefaction of elastic fibers. We report a sporadic case of acrokeratoelastoidosis in a 13-year-old girl and review the etiology, differential diagnosis, and treatment of this disorder.